﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  207 
  

  

  Detailed 
  investigations 
  will 
  have 
  to 
  decide 
  whether 
  

   in 
  the 
  foregoing 
  discussion 
  imagination 
  has 
  been 
  led 
  to 
  

   falsely 
  group 
  together 
  heterogeneous 
  phenomena 
  or 
  not. 
  

   We 
  should, 
  of 
  course, 
  never 
  lose 
  sight 
  of 
  the 
  fact 
  that 
  the 
  

   working 
  of 
  the 
  principle 
  is 
  very 
  different 
  in 
  the 
  different 
  

   cases. 
  The 
  conception, 
  however, 
  of 
  the 
  tendency 
  of 
  two 
  

   substances 
  in 
  moving 
  past 
  each 
  other 
  to 
  form 
  a 
  surface 
  of 
  

   contact 
  which 
  offers 
  a 
  minimum 
  of 
  resistance 
  by 
  substi- 
  

   tuting 
  a 
  rhythm 
  for 
  uniform 
  motion 
  is 
  of 
  fundamental 
  

   value. 
  This, 
  however, 
  is 
  itself 
  but 
  a 
  special 
  case 
  of 
  a 
  still 
  

   broader 
  conception, 
  that 
  of 
  the 
  principle 
  of 
  least 
  work, 
  

   which 
  according 
  to 
  H. 
  von 
  Helmholtz 
  84 
  is 
  probably 
  as 
  

   general 
  a 
  law 
  of 
  nature 
  as 
  that 
  of 
  the 
  preservation 
  of 
  

   energy. 
  

  

  VII. 
  Nomenclature. 
  

  

  The 
  term 
  "Sedimentary 
  Ripples" 
  which 
  appears 
  in 
  

   the 
  title 
  of 
  this 
  paper, 
  may 
  now 
  be 
  denned 
  to 
  include 
  all 
  

   undulating 
  surface 
  forms 
  which 
  originate 
  as 
  surfaces 
  of 
  

   least 
  friction 
  or 
  parts 
  of 
  such 
  along 
  the 
  contact 
  of 
  a 
  

   moving 
  fluid 
  and 
  an 
  unconsolidated 
  sediment, 
  with 
  their 
  

   crests 
  trending 
  at 
  right 
  angles 
  or 
  obliquely 
  to 
  the 
  direc- 
  

   tion 
  of 
  flow 
  of 
  the 
  fluid. 
  This 
  definition 
  excludes 
  all 
  such 
  

   undulations 
  as 
  form 
  at 
  the 
  contact 
  of 
  two 
  layers 
  of 
  rock, 
  

   for 
  instance, 
  the 
  corrugations 
  found 
  on 
  the 
  cleavage 
  faces 
  

   of 
  slate 
  or 
  the 
  peculiar 
  variety 
  of 
  mudflow 
  structure 
  

   imitating 
  ripples, 
  which 
  was 
  described 
  by 
  Fuchs 
  85 
  from 
  

   the 
  lower 
  surfaces 
  of 
  "Fly 
  sen" 
  sandstones 
  and 
  proven 
  

   experimentally 
  to 
  form 
  when 
  a 
  viscous 
  mass 
  (like 
  plaster 
  

   of 
  Paris) 
  flows 
  over 
  a 
  yielding 
  substratum 
  (like 
  sand). 
  

   Such 
  forms 
  might 
  be 
  referred 
  to 
  as 
  "Pseudo-ripples." 
  

  

  It 
  also 
  includes 
  beach-cusps 
  and 
  other 
  longitudinal 
  sur- 
  

   face 
  structures, 
  for 
  instance, 
  longitudinal 
  dunes. 
  The 
  

   word 
  "dunes" 
  would 
  be 
  preferable 
  to 
  "ripples" 
  as 
  a 
  

   general 
  term, 
  as 
  suggested 
  by 
  Gilbert, 
  but 
  its 
  firmly 
  

   established 
  usage 
  which 
  includes 
  all 
  kinds 
  of 
  wind-shaped 
  

   hills 
  prevents 
  such 
  a 
  redefinition. 
  The 
  terms 
  used 
  in 
  this 
  

   paper 
  for 
  the 
  different 
  types 
  of 
  "sedimentary 
  ripples" 
  

   and 
  their 
  classification, 
  are 
  given 
  in 
  the 
  following 
  table. 
  

  

  84 
  H. 
  von 
  Helmholtz, 
  Wissenschaftliche 
  Abhandlungen, 
  vol. 
  3, 
  p. 
  209-210 
  

   (Ueber 
  die 
  physikalische 
  Bedeutung 
  des 
  Prinzips 
  der 
  kleinsten 
  Wirkung). 
  

  

  85 
  Theodor 
  Fuchs, 
  Studien 
  ueber 
  Fucoiden 
  and 
  Hieroglyphen, 
  K. 
  Akad. 
  

   Wiss., 
  Wien, 
  vol. 
  62, 
  pp. 
  371-374, 
  1895. 
  

  

  